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arXiv 2104.14604cond-mat.softcond-mat.dis-nncond-mat.mtrl-sci
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锂盐基深共晶溶剂:玻璃形成和转动-平移耦合对离子电荷输运的重要性

Lithium-salt-based deep eutectic solvents: Importance of glass formation and rotation-translation coupling for the ionic charge transport

A. Schulz, P. Lunkenheimer, A. Loidl

摘要:

基于锂盐的深共熔溶剂,其中唯一的阳离子是Li+,是作为电化学储能设备如电池中的电解质的有前途的候选者。我们已经进行了宽带介电谱三个这样的系统,涵盖了广泛的温度和动态范围,从低粘度的液体在室温下的玻璃态接近玻璃化转变温度。我们检测到的弛豫过程,可以归因于偶极重取向动力学,并表现出明确的签名玻璃冻结。我们发现离子直流电导率的温度依赖性及其室温值也受这些系统的玻璃态动力学的支配,例如,玻璃化转变温度和脆性。与先前研究的相应系统相比,含有氯化胆碱而不是锂盐,由于玻璃化转变温度的变化和锂离子的较高离子电势,重取向和离子动力学都显着降低。这些锂基深共晶溶剂部分表现出显着的偶极重取向和离子平移动力学的解耦,并大致遵循分数Debye-Stokes-Einstein关系,导致直流电导率的增强,特别是在低温下。所提出的结果清楚地揭示了去耦效应的重要性和这些系统的典型的玻璃形成性能的技术相关的室温电导率。

英文摘要:

Lithium-salt-based deep eutectic solvents, where the only cation is Li+, are promising candidates as electrolytes in electrochemical energy-storage devices like batteries. We have performed broadband dielectric spectroscopy on three such systems, covering a broad temperature and dynamic range that extends from the low-viscosity liquid around room temperature down to the glassy state approaching the glass-transition temperature. We detect a relaxational process that can be ascribed to dipolar reorientational dynamics and exhibits the clear signatures of glassy freezing. We find that the temperature dependence of the ionic dc conductivity and its room-temperature value also are governed by the glassy dynamics of these systems, depending, e.g., on the glass-transition temperature and fragility. Compared to the previously investigated corresponding systems, containing choline chloride instead of a lithium salt, both the reorientational and ionic dynamics are significantly reduced due to variations of the glass-transition temperature and the higher ionic potential of the lithium ions. These lithium-based deep eutectic solvents partly exhibit significant decoupling of the dipolar reorientational and the ionic translational dynamics and approximately follow a fractional Debye-Stokes-Einstein relation, leading to an enhancement of the dc conductivity, especially at low temperatures. The presented results clearly reveal the importance of decoupling effects and of the typical glass-forming properties of these systems for the technically relevant room-temperature conductivity.

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